With the breakthrough of the third generation of semiconductor material gallium nitride and the birth of blue, green and white light-emitting diode, LED (Light-Emitting Diode), which is praised as “a technique lighting the future”, gradually comes into our daily life, and will lead us to a brighter future. Using the third generation of semiconductor material gallium nitride as a semiconductor lighting source, the electric power consumption is only 1/10 of incandescent lamp under the same brightness, and the service life can reach 80,000 hours or more. A semiconductor lamp can use 50 years or more under normal circumstance. As a novel lighting technique, LED will initiate a revolution in lighting field due to its advantages of versatile application, environmental friendly and convenient adjustment. The emergence of white light LED is a substantial step LED strides from marking function to lighting function. White light LED is closest to sunlight and can reflect the real color of radiated object more precisely. Seen from technical point of view, white light LED is undoubtedly the most top-edge technique of LED. The application market of white light LED will be very broad. Therefore, it is needed for a high efficiency phosphor capable of effectively converting the light from ultraviolet light to green light emitted by a light-emitting element including LED into visible light, so as to achieve white light system and multicolor system lighting device.
At present, in prior art field, white light LED is achieved mainly by a method of exciting phosphor by using ultraviolet chip or blue light chip. However, the method is always limited by the limitation of phosphors.
For example, the patents U.S. Pat. Nos. 5,998,925, 6,998,771 and ZL00801494.9 all use blue light chip to excite cerium activated rare-earth garnet phosphor (e.g., Y3A15012:Ce, (Y, Gd)3(Al, Ga)5012:Ce, YAG for short; or Tb-garnet, TAG for short), wherein the phosphors are excited by blue light chip to emit yellow light which is blended with part of the blue light from blue light chip into white light. In this process, the used phosphors are confined greatly with respect to the application and performance of white light LED. First, the excitation of this phosphor is within the range of 420-490 nm, the most effective excitation is within the range of 450-470 nm, it is not excited within ultraviolet light region and the short wavelength side region of visible light as well as green light region; second, the emission spectrum of the phosphor of the rare-earth garnet structure can only reach at most about 540 nm, lacking red component, and thereby resulting in lower color rendering index of white light LED.
For example, the patents U.S. Pat. No. 6,649,946, US 20040135504, CN1522291A, CN1705732A, CN1596292A, CN1596478A, and U.S. Pat. No. 6,680,569A relate to rare-earth activated nitride or oxynitride phosphor capable of being effectively excited in UV-blue light region. The effective excitation wavelength range of the phosphor of this process is somewhat increased, and the emission range can also be from green light to red light, but the luminescent brightness of the phosphor is low, moreover, their production cost is high. Hence, the phosphors are confined greatly as practical LED fluorescent powder.
For example, U.S. Pat. No. 6,351,069 concerns sulfide phosphors in red color. The phosphor can be added to white light LED as a complementary color component to compensate color rending index and reduce color temperature. However, sulfide phosphors are low in luminescent brightness, although they improve color rendering index, they also reduce the lumen efficiency of LED; further, they are poor in chemical stability and aging characteristics, and corrode chips, shortening the service life of LED.
For example, US 20060027781, US 20060028122 and US 20060027785 relate to silicate phosphor, but the materials are confined within the structure of barium-containing metasilicates. Moreover, their excitation spectrum are within the range of 280-490 nm, emission spectrum within the range of 460-590 nm, and have a luminescence only in the range from green color to yellow color, also lacking red light. Further, the phosphors are poor in luminescent intensity and cannot match YAG phosphor.
For example, CN1585141A relates to halosilicate phosphor in green color and disilicate and metasilicate phosphor in red color. The phosphor in green color described in the patent is broad with respect to excitation spectrum, but unitary in luminescent color; moreover, said phosphor in red color are poor in luminescent intensity and cannot match the fluorescent powder in the prior art, and hence are confined greatly in practical application.